Etching method of organic insulating film

ABSTRACT

This invention relates to a method for etching an organic insulating film used in the production of semiconductor devices.  
     A sample to be etched on which a low dielectric constant organic insulating film is formed is etched by generating a plasma from hydrogen gas and nitrogen gas or ammonia gas, and controlling the gas flow rate and pressure so that the light emission spectral intensity ratio of hydrogen atom and cyan molecule in the plasma comes to a prescribed value. By this method, a low dielectric constant organic insulating film as an insulating film between layers can be etched without using any etch stop layer so that bottom surfaces of trenches and holes for electrical wiring become flat.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to an etching method of organic insulatingfilms, and particularly to an etching method suitable for etchingorganic insulating films used in the production of semiconductordevices.

[0003] 2. Description of the Related Art

[0004] [Prior Art 1]

[0005] As a method for etching an organic insulating film whilepreventing the microtrenching without using etch stop layer, forexample, the method of WO 01/15213 A1 (JP-A-2001-60582) is known. Thegazette of the above-mentioned patent gives the following description.

[0006] Thus, the wafer temperature is maintained at 20-60° C., inaccordance with the processing. Then, a gaseous mixture of N₂, H₂ and Aris introduced into the processing chamber. The inner pressure of theprocessing chamber is adjusted to 500 mTorr or more substantially, andpreferably 500-800 mTorr substantially. Then, a radio-frequency voltagehaving a frequency of 13.56 MHz and a power of 600-1,400 W is applied tothe lower electrode, and a radio-frequency power having a frequency of60 MHz and a power of 600-1,400 W is applied to the upper electrode. Bytaking such a measure, a high-density plasma is generated in theprocessing chamber and, due to the plasma, contact holes of a desiredshape are formed in the insulating layer between layers of wafer made ofan organic low-dielectric constant material.

[0007] Further, the same gazette as above makes the following mention,too.

[0008] A treating gas containing at least a nitrogen atom-containing gasand a hydrogen atom-containing gas is introduced into the processingchamber, and the inner pressure of the vacuum processing chamber isadjusted substantially to 500 mTorr or more to carry out etching of theorganic layer film formed on the wafer to be etched placed in theprocessing chamber. As the material constituting the organic film, alow-dielectric constant material having a relative permittivity of 3.5or less is preferable. The inner pressure of the vacuum processingchamber is preferably kept at 500-800 mTorr substantially.

[0009] By using a gas containing at least a nitrogen atom-containing gasand a hydrogen atom-containing gas as the processing gas and adjustingthe inner pressure of the vacuum processing chamber substantially to 500mTorr or higher, microtrenching can be prevented without using etch stoplayer and the mask-selection ratio can be enhanced. Such a technique isespecially effective for processes which require to stop the etching inthe midst of an organic layer film, such as the dual damascene process,or the like.

[0010] It is possible to use N₂ as the nitrogen atom-containing gas orto use H₂ as the hydrogen atom-containing gas, if desired. In thegazette referred to above, there are mentioned some examples in whichthe N₂/H₂ flow rate ratio (N₂/H₂) is 400 sccm/400 sccm, 200 sccm/200sccm, and 100 sccm/300 sccm.

[0011] [Prior Art 2]

[0012] As another method for etching an organic insulating film, themethod of JP-A-2000-252359 is known. The following description is givenin the gazette thereof.

[0013] An insulating film (insulating film) between layers made of anorganic dielectric film such as polyallyl ether is subjected to etching,while forming a CN group-containing reaction product, etc. by the use ofan NH group-containing ion or radical generated from a gas plasma madefrom a mixture of hydrogen and nitrogen or an ammonia-containing gas.

[0014] The etching process of the insulating film between layers iscarried out by means of ECR type (Electron Cyclotron Resonance type)plasma etching apparatus under conditions of, for example, asubstrate-provided electrode temperature of 20° C., a μ-wave power (2.45GHz) of 2,000W, a pressure of 0.8 Pa, an RF power of 300 W, by using NH₃as an etching gas at a flow rate of 100 sccm.

[0015] In the etching process mentioned above, it is also possible, ifdesired, to carry out the etching process by the use of a gas plasmacomprising a gaseous mixture of hydrogen and nitrogen at a flow rate(N₂+H₂) of, for example, 100 sccm at a H₂/N₂ flow rate ratio of, forexample, 75/25 sccm.

[0016] By carrying out the etching using NH group-containing ion orradical, an insulating film containing an organic dielectric film can besubjected to an anisotropic etching without forming a damage layercausing defective conduction, while suppressing side etching, whilemaintaining a high etch rate of about 450 nm/minute, without bringingabout a reduction of throughput, and rapidly.

[0017] By such a technique, it is also possible to etch an insulatingfilm containing an organic insulating film to open contact holes. Thistechnique is applicable also to an etching process for forming trenchfor interconnect wiring such as damascene process, or to an etchingprocess for simultaneously opening trench for interconnect wiring andcontact hole such as dual damascene process, etc.

[0018] Further, if etching process of insulating film between layers iscarried out under various conditions [(a) N₂=100 sccm, (b) N₂/H₂=50/50sccm and (c) H₂=100 sccm] and emission spectra are measured, an NH peakobservable neither in the case (a) using N₂ gas nor in the case (c)using H₂ gas is observed in the case (b) using N₂/H₂ mixture. Further,as for CN peak, the peak intensity observed in the case (b) using N₂/H₂mixture is higher than the peak intensity in the case (a) using N₂ gasand in the case (c) using H₂ gas.

[0019] Further, if the flow rate ratio of etching gas is so varied thatN₂/H₂=100/0 to 50/50 to 0/100 sccm and the relative etch rate (the etchrate at N₂/H₂=100/0 sccm is taken as 1) and the emission spectralintensity ratios between the light-emitting components (CN, NH, N₂, CH,H) at varied flow rate ratios are measured, it is found that the etchrate and the emission spectral intensity ratio between CN and NH areroughly the same in the behavior.

`SUMMARY OF THE INVENTION

[0020] In the recent years, a damascene process using copper has beenused as a method for forming a wiring on semiconductor elements. As anapplication of the damascene process, a dual damascene process can bereferred to. In the prior dual damascene, an etch stop layer has beenused for preventing the sub-trenching which is sometimes called“microtrenching”, at the time of forming a trench for interconnectwiring leading to the organic insulating film functioning as aninsulating film between layers. Since an etch stop layer has a highdielectric constant, however, it is attempted today to lower thedielectric constant without using any etch stop layer.

[0021] According to the former prior art mentioned above(JP-A-2001-60582), etching of organic layer film is performed whilekeeping the inner pressure of vacuum processing chamber at 500 mTorr(ca. 66.5 Pa) or above, and preferably at 500-800 mTorr. According tothis etching method, however, inner pressure of the processing chamberis very high, and hence this method is expected to have the followingproblems: (1) in the case of samples having a large diameter such as 300millimeter wafer, the waste gas generated as a reaction product from thewafer surface cannot sufficiently be removed at the central part ofwafer, so that the etch rate within the wafer surface is not uniform,(2) the quantity of reaction product is so large that controlling theshape of trench and hole is difficult, and (3) the quantity of reactionproduct is so large that inside of processing chamber is apt to besoiled, which reduces reproducibility of the etching treatment.Accordingly, a measure for solving these problems have to be taken whenthe processing is to be carried out at a high processing pressure.

[0022] On the other hand, the latter prior method (JP-A-2000-252359) isknown as a method for etching an organic insulating film at a lowprocessing pressure (0.8 Pa) which makes it unnecessary to consider theabove-mentioned problems in the etching process at a high processingpressure. The latter prior method, however, pays no consideration forthe problem occurring when an organic insulating film of dual damasceneprocess is etched while preventing microtrenching without using etchstop layer.

[0023] According to the latter prior art, an organic insulating film isetched with an NH group-containing ion or radical generated by gasdischarge or the like in a hydrogen-nitrogen gas mixture or ammonia gasmixture as a processing gas, while forming a CN group-containingreaction product, etc. However, this technique is unable to prevent themicrotrenching without using etch stop layer at any flow rate ratio ofhydrogen-nitrogen mixed gas or ammonia-containing gas.

[0024] The etching method of the latter prior art is a method in whichattention is paid to the fact that etch rate and CN/NH emission spectralratio are roughly the same in behavior. Accordingly, this method has aproblem that the optimum condition of etching cannot be selected on thebasis of CN/NH emission spectral intensity ratio, and the optimumcondition for etching an organic insulating film while preventingmicro-trenching without using etch stop layer cannot be selected.

[0025] The phenomenon that a microtrenching (sometimes called“sub-trenching”, too) is formed and thereby the bottom surface of thetrenches or holes of the etched part become impossible to flatten isattributable to the following fact. The etch rate is higher in theneighborhood of sidewall of trenches and holes than in the central partsof the trenches and holes due to collision of the incident ionoriginated from the plasma against the sidewall, caused by the slighttaper of the sidewall of trenches and holes which are the part to beetched, followed by concentration of the incident ion into theneighborhood of sidewall of trenches and holes, or due to are-deposition of various reaction products formed by the etching to thecentral parts of trenches and holes.

[0026] It is an object of this invention to solve the problems mentionedabove by providing an etching method of organic insulating film whichmakes it possible to perform etching of an organic insulating film whilesuppressing the re-deposition of reaction products onto inner walls ofprocessing chamber and preventing the microtrenching.

[0027] The above-mentioned object can be achieved by an etching methodof organic insulating film which comprises generating a plasma from amolecular gas containing hydrogen atom and nitrogen atom, measuring theemission spectral intensity ratio between hydrogen atom and cyanmolecule in the plasma, and carrying out the processing while keepingthe measured value of the ratio at a prescribed value or under.

[0028] In this invention, there is used a plasma in which the emissionspectral intensity ratio CN/H between the emission spectrum of hydrogen(H) at a wavelength of about 486 nm and that of cyan molecule (CN) at awavelength of about 388 nm is 1 or less.

[0029] Further, the above-mentioned object can be achieved by generatinga plasma from hydrogen gas and nitrogen gas or ammonia gas, andperforming an etching method of organic insulating film whilecontrolling the flow rate of hydrogen gas so that the emission spectralintensity ratio between hydrogen atom and cyan molecule in the plasmacomes to a prescribed value or under.

[0030] The processing is carried out while controlling the processingpressure at a constant value.

[0031] Further, the above-mentioned object can be achieved by supplyinga nitrogen gas and a hydrogen gas or a molecular gas containing hydrogenatom and nitrogen atom into an etching process chamber in which isplaced a sample to be etched forming an organic insulating film,adjusting the inner pressure of the etching process chamber to apressure lower than 10 Pa, thereby generating a plasma in which theintensity ratio CN/H between an emission spectrum of hydrogen atom (H)at a wavelength of about 486 nm and an emission spectrum of cyanmolecule (CN) at a wavelength of 388 nm is 1 or less, and processing thesample to be etched with said plasma.

[0032] For generating of the plasma, a hydrogen gas and a nitrogen gasare used, and the mixing ratio of the hydrogen gas to the nitrogen gasis adjusted to 10 or more. Further, total flow rate of the hydrogen gasand nitrogen gas is adjusted to 200 cc/minute or more.

[0033] Alternatively, a hydrogen gas is used as the molecular gascontaining hydrogen atom, an ammonia gas is used a the molecular gascontaining nitrogen atom, and the mixing ratio of the hydrogen gas tothe ammonia gas is adjusted to 10 or more. Further, the total flow rateof the hydrogen gas and the ammonia gas is adjusted to 200 cc/minute ormore.

[0034] According to another embodiment of this invention, theabove-mentioned object can be achieved by generating a plasma in theprocess chamber, measuring the emission spectral intensity ratio betweencyan molecule and hydrogen atom in the plasma, controlling the flowrate-controlling valves so as to keep the measured value at a prescribedvalue or under, and etching the sample to be etched, by the use of anapparatus equipped with a sample stand on which a sample to be etchedcan be placed, an air-leakless process chamber into which an etching gasis fed, a vacuum pump evacuating the inner space of process chamber to areduced pressure, flow rate-controlling valves which can control theflow rates of hydrogen gas and nitrogen gas or a molecular gascontaining hydrogen atom and nitrogen atom, a gas exhaustrate-controlling valve which is placed between the vacuum pump and theprocess chamber to control the exhaust rate of the etching gas fed intothe process chamber, a circuit and an electric source to which theelectric power for generating a plasma from the etching gas in theprocess chamber can be applied, and a vacuum gauge for measuring thepressure in the process chamber. The flow rate-controlling valves arecontrolled so as to increase the flow rate of hydrogen gas. Further, thegas exhaust rate-controlling valve is controlled so as to keep constantthe inner pressure of the process chamber.

[0035] The sample to be etched is etched while controlling the output ofelectric source for generating a plasma from the etching gas so as tokeep the measured value at a prescribed value or under. The electricsource is controlled so as to increase the output and thereby toincrease generation of hydrogen atom in the plasma.

[0036] Further, an electric source capable of inputting a bias voltageto the sample to be etched is connected to the sample stand, and theelectric source is controlled so as to lower the bias voltage andthereby keep the measured value at a prescribed value or under.

[0037] Other objects, features and advantages of the invention willbecome apparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a longitudinal cross sectional view illustrating oneexample of the etching apparatus for carrying out the etching method ofthis invention.

[0039]FIG. 2 is a plan view illustrating the whole of the plasma etchingapparatus provided with the etching apparatus of FIG. 1.

[0040]FIG. 3 is a flow chart illustrating an etching process using theapparatus of FIG. 2.

[0041]FIG. 4 is a longitudinal cross sectional view illustrating theshape of cross section of etching of a wafer according to the etchingflow shown in FIG. 3.

[0042]FIG. 5 is a figure illustrating the light emission intensity of aplasma in the subtrench-free etching process in an interconnect wiringtrench processing of an organic insulating film.

[0043]FIG. 6 is a figure illustrating the light emission intensity of aplasma in a subtrench-forming etching process in an interconnect wiringtrench processing of an organic insulating film.

[0044]FIG. 7 is a cross sectional view illustrating the shape of crosssection of etching which has been subjected to etching in the state ofthe plasma light emission intensity shown in FIG. 5.

[0045]FIG. 8 is a cross sectional view illustrating the shape of crosssection of etching which has been subjected to etching in the state ofthe plasma light emission intensity shown in FIG. 6.

[0046]FIG. 9 is a figure illustrating the relation between the lightemission intensity ratio CN/H between cyan molecule and hydrogen atom ina plasma and sub-trenching, in an interconnect wiring trench processingof an organic insulating film.

[0047]FIG. 10 is a chart illustrating the flow for suppressing thesub-trenching in an interconnect wiring trench processing of an organicinsulating film.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] Hereunder, one example of this invention is explained byreferring to FIGS. 1 to 10.

[0049]FIGS. 1 and 2 illustrate one example of the plasma etchingapparatus for carrying out the etching method of this invention, whereinFIG. 1 illustrates an outlined construction of the etching processchamber, and FIG. 2 illustrate the whole of the plasma etching apparatusprovided with the etching process chamber of FIG. 1.

[0050] In the vacuum chamber 11, a sample stage 24 is provided, on whichwafer 2, namely a sample to be etched, can be set. The sample stage 24is connected to a high-frequency electric source 25 (for example,frequency 800 kHz) for bias voltage which gives a bias voltage to wafer2. Sample 24 is connected also to a temperature controlling apparatus 26for controlling the temperature of wafer 2.

[0051] In the upper part of the vacuum container 11 is formed acylindrical process chamber. Outside the process chamber of the vacuumchamber 11 is provided magnetic field-generating coils 23 a and 23 b soas to envelop the process chamber. In the upper part of the processchamber in the vacuum chamber 11 is provided a plate antenna 13 composedof an electroconductive material so as to confront the sample stage 24through intermediation of a dielectric body 12 through which anelectromagnetic field can propagate. In the upper part of the plateantenna 13 is provided a coaxial line 15, via which the antenna isconnected to a high-frequency electric source 16 (for example, frequency450 MHz) for generating a plasma.

[0052] On the plate antenna 13 is formed a gas feeding line 14 having athrough-holes for supplying an etching gas into the process chamber. Thegas feeding line 14 is connected to gas tanks 20, 21 and 22 via flowrate controlling valves 17, 18 and 19, respectively.

[0053] In the bottom part of the vacuum chamber 11 is provided a vacuumgas exhaust hole, which is connected to vacuum pump 28 via gas exhaustrate controlling valve 27.

[0054] In the process chamber part of the vacuum chamber 11, there isprovided a spectro-photoelectric converter 30, which detects the lightemitted from the plasma 32 formed between the plate antenna 13 andsample stage 24 and converts a light of specified wavelength to electricsignals. The electric signals emitted from the spectro-photoelectricconverter 30 is input to controller 31. The controller 31 carries out acalculation mentioned later, and outputs the electric signals forcontrolling the flow rate controlling valves 17, 18 and 19 and thehigh-frequency electric sources 16 and 25. The vacuum chamber 11 isprovided with vacuum gauge 29. Although not shown in the figures, thedetected signals are input to the controller 31, and the controller 31controls the gas exhaust rate controlling valve 27.

[0055] The etching process chamber having the construction of FIG. 1 isset around the vacuum carrying chamber 6 as shown in FIG. 2, as etchingprocess chambers 10 a and 10 b. Around the vacuum carrying chamber 6 areprovided load lock chamber 5 a and unload lock chamber 5 b. The loadlock chamber 5 a and unload lock chamber 5 b are connected toatmospheric air unit 3. The atmospheric air unit 3 is provided withatmospheric air carrying robot 4, and wafer 2 is carried by the aircarrying robot 4 between cassette 1 a or 1 b and load lock chamber 5 aor unload lock chamber 5 b. The vacuum carrying chamber 6 is providedwith a vacuum carrying robot 7, and wafer 2 is carried by the vacuumcarrying robot 7 between the load lock chamber Sa or unload lock chamber5 b and etching process chamber 10 a or 10 b.

[0056] In the apparatus having the above-mentioned construction, wafer 2is carried from the cassette 1 a, for example, into etching processchamber 10 a as shown at FIG. 2. After carrying the wafer 2, the wafer 2is held on the sample stage 24, and set to a position of prescribedheight by the stage which can move upward and downward. The wafer 2 ismaintained at a prescribed temperature by a sample temperature controlequipment. After reducing the inner pressure of vacuum chamber 11 by theuse of vacuum pump 28, the flow rate controlling valves 17, 18 and 19are controlled to introduce the process gas (etching gas in this case)into the process chamber from the gas feeding sources 20, 21 and 22 viathe gas feeding line 14, and adjusted to a desired pressure. Afteradjustment of pressure in the process chamber, a high-frequency power (ahigh-frequency power of 450 MHz, for example) is oscillated fromhigh-frequency electric source 16. The high-frequency power oscillatedfrom the high-frequency electric source 16 propagates through thecoaxial line 15 and is introduced into the process chamber via plateantenna 13 and dielectric body 12. The electric field of thehigh-frequency electric power introduced into the process chambergenerates a plasma 32 at a low pressure in the process chamber, throughinteraction with the magnetic field formed in the process chamber by themagnetic field-generating coils 23 a and 23 b, such as solenoid coils.When a magnetic field having a strength capable of inducing an electroncyclotron resonance effect (for example, 160 G) is formed in the processchamber, a plasma can be generated especially efficiently.Simultaneously with generation of plasma, a high-frequency power havinga frequency of, for example, 800 KHz, is input to the sample stage 24 bythe high-frequency electric source 25. By this, an incident energy intowafer 2 is given to the ion in plasma 32, the ion enters the wafer 2,and an anisotropic etching of wafer 2 is promoted.

[0057] Next, an etching process of insulating film between layerscomposed of an organic insulating film used in the dual damasceneprocess using the above-mentioned apparatus will be explained byreferring to FIGS. 3 and 4.

[0058] First, an unprocessed wafer 2 is carried into the first etchingprocess chamber 10 a (Step 101). At this time, the unprocessed wafer 2is in a state that, as shown in FIG. 4(a), a patterned photoresist isformed on an unprocessed hard mask 45. The wafer 2 is in a state that amultilayer interconnect wiring is formed on a substrate, provided thatin this case the underlayer organic insulating film 41 (insulating filmbetween layers), underlayer interconnect wiring 42 and underlayer hardmask layer 43 have already been processed. On the underlayer hard mask43, an organic insulating film 44 which is an interlayer insulating filmto be processes from now (an organic film having a low dielectricconstant of 2.6-2.7, such as SiLK™ manufactured by Dow Chemicals) and ahard mask 45 (in this case, a dual hard mask made of SiN film/SiO₂ film)are formed in the form of films. As an uppermost layer, a patternedphotoresist 46 is formed.

[0059] Next, a process gas for hard mask etching (for example, Ar+O₂+CFgas (C₅F₈)) is fed into the process chamber of the first etching processchamber 10 a, and a plasma etching is carried out. In this etchingprocess, a mask for processing the connection holes for etching theorganic insulating film 44 is formed (Step 102).

[0060] In the etching process of hard mask 45, the completion of etchingis detected by the end point detection using emission spectroscopicanalysis (Step 103). FIG. 4(b) illustrates a cross section of processingof the etched material. At this point in time, photoresist 46 mayremain.

[0061] Next, wafer 2 which has completed the processing of hard mask 45is carried to the second etching chamber 10 b (Step 104).

[0062] In the second etching process chamber lob, a process gas foretching of organic insulating film (ammonia NH₃) is fed into the processchamber to perform a plasma etching. In this etching process, contactholes with underlayer interconnect wiring 42 are formed on the organicinsulating film 44 (Step 105). The photoresist remaining from thepreceding step is composed of fundamentally identical components withthe organic insulating film, and hence it is also etched off in theetching process of this step.

[0063] In the etching process of organic insulating film 44, thecompletion of etching is detected by the end point detection usingemission spectroscopic analysis (Step 106). FIG. 4(c) illustrates thecross section of processing of the etched material. At this time,photoresist 46 has been removed, so that the connection hole 47 reachesthe underlayer interconnect wiring 42.

[0064] The wafer 2 which has completed the etching processing of organicinsulating film 44 is returned into the original cassette 1 a (Step107).

[0065] When all the wafers 2 in the cassette 1 a have been processed andreturned into cassette 1 a as above, a preparation for processing theinterconnect wiring trench on the organic insulating film 44 is started.Cassette 1 a containing the wafers 2 which have completed the processingof contact hole 47 are sent to other apparatus, such as washingapparatus, resist-coating apparatus, light-exposing apparatus,developing apparatus, etc. By these apparatuses, a photoresist in whicha pattern of wiring trench is patterned on hard mask 45 is formed onwafer 2 in the cassette 1 a (Step 108).

[0066] Subsequently, cassette 1 a containing the wafer 2 having thepatterned photoresist thereon is set to the atmospheric air unit 3 ofthe plasma etching apparatus (Step 111).

[0067] After setting the cassette 1 a, wafer 2 is carried into the firstetching process chamber 10 a (Step 112). At this time, the wafer 2 has apatterned photoresist 48 formed on hard mask 45, as shown in FIG. 4(d).

[0068] Subsequently, the same process gas for hard mask etching as inStep 102 (for example, Ar+O₂+CF gas (C₅F₈)) is fed into the processchamber of the first etching process chamber 10 a to carry out a plasmaetching. In this etching treatment, a mask for processing of wiringtrench for etching the organic insulating film 44 is formed (Step 113).

[0069] Completion of the etching processing of hard mask 45 is detectedby the end point detection by emission spectroscopic analysis (Step114). FIG. 4(e) shows the cross section of processing of the etchedbody. In hard mask 45, openings for wiring trenches of which openingdiameter is greater than that of contact hole 47 are formed. At thispoint in time, photoresist 46 may remain.

[0070] Subsequently, the wafer 2 which has completed the processing ofhard mask 45 is carried into the second etching process chamber 10 b(Step 115).

[0071] A process gas for the etching treatment of organic insulatingfilm (hydrogen gas (H₂)+nitrogen gas (N₂)) is fed into the processchamber of the second etching process chamber 10 b to carry out a plasmaetching. By this etching process, a wiring trench having a prescribeddepth is formed in the organic insulating film 44 (Step 116). Since thisetching process uses no etching stopper layer, flattening of the etchingbottom surface is important and, at the same time, uniformity of etchdepth within the wafer is important. The conditions of process and themethod for controlling the process in this etching process will bementioned later. The photoresist 48 remaining from the preceding step isetched off altogether in the etching process of this step, in the samemanner as above.

[0072] Completion of the etching processing of organic insulating film44 is detected by an end point detecting method such as mentioned inU.S. patent application Ser. No. 09/946,504 (JP Application 2001-28098)which comprises using a wavelength pattern of differentiated value ofinterference light, measuring the film thickness from the standardpattern and the actual pattern at the time of actual processing andcalculating the depth of etching (Step 117). FIG. 4(f) illustrates thecross section of processing of the etched body. At this point in time,photoresist 46 has been removed, and wiring trench 49 having aprescribed depth is formed.

[0073] The wafer 2 which has completed the etching processing of organicinsulating film 44 is returned into the original cassette 1 a (Step118).

[0074] By carrying out the steps mentioned above, a processing oforganic insulating film according to dual damascene process can be putinto practice. With the plasma etching apparatus of the present example,two etching process chambers can be used, and therefore the etching ofhard mask 45 for processing of contact hole and the etching of organicinsulating film 44 can be carried out continuously. Further, the etchingof hard mask 45 for processing of wiring trench and the etching oforganic insulating film 44 can be carried out continuously by merelychanging over the process gas of the second etching process chamber.Thus, a processing of organic insulating film according to dualdamascene process can be performed with only one apparatus.

[0075] Further, if three etching process chambers are provided aroundthe vacuum carrying chamber 6 so as to carry out the etching of hardmask 45 for contact holes and wiring trenches at the second processchamber placed at the central position, the etching of the contact holesof the organic insulating film 44 at the first etching process chamberplaced in the neighborhood (for example, on the left side) of the secondetching process chamber, and the etching of the wiring trenches oforganic insulating film 44 at the third etching process chamber placedin the neighborhood (for example, on the right side) of the secondetching process chamber, the processes of the respective etching processchambers can be fixed. Further, it is also possible to use the secondand first etching process chambers alternately to carry out a continuousprocess with the second and first etching process chambers or with thesecond and third etching process chambers. By taking such a measure, itbecomes possible to store the wafers for contact holes in cassette 1 aand the wafers for wiring trenches in cassette 1 b and thereby to carryout the etching of the contact holes and wiring trenches simultaneouslywith only one apparatus (simultaneous processing).

[0076] Further, if four etching process chambers are provided around thevacuum carrying chamber 6, the etching of the hard mask 45 for contactholes and etching of the contact holes of organic insulating film 44 canbe carried out continuously at respective process chambers for exclusiveuse, by the use of the first and second etching process chambers; andthe etching of the hard mask 45 for wiring trenches and etching of thewiring trenches of organic insulating film 44 can be carried outcontinuously at respective process chambers for exclusive use, by theuse of the third and fourth etching process chambers. By taking such ameasure, it becomes possible to store the wafers for contact holes incassette 1 a and the wafers for wiring trenches in cassette 1 b andthereby to carry out the etching of the contact holes and wiringtrenches in parallel with only one apparatus.

[0077] In the present example, the load rock chamber 5 a isdistinguished from unload rock chamber 5 b. However, it is also possibleto use the rock chamber 5 a for carrying in and carrying out the wafersof cassette 1 a and to use the rock chamber 5 b for carrying in andcarrying out the wafers of cassette 1 b. By taking such a measured, thecarrying route of wafers can be made shortest in the above-mentionedsimultaneous and in-parallel processes in the cases of providing threeor four etching process chambers.

[0078] Subsequently, the etching method of wiring trenches of organicinsulating film 44 in the above-mentioned Step 116 will be explained byreferring to FIGS. 5 to 10.

[0079] In the etching of wiring trench, the etching characteristics wereevaluated for the five cases shown in Table 1. TABLE 1 Gas flow rate(cc/min) Inner pressure Etch CN/H Hydrogen Nitrogen Ammonia of processrate intensity Sub-trench Case gas gas gas chamber (Pa) (nm/min) ratiocoefficient 1 200 10 0 3 122 0.6 96 2 200 0 20 3 154 0.7 100 3 50 50 0 3159 4.5 122 4 50 0 50 3 189 6 126 5 200 10 0 10 127 3.7 120

[0080] In Cases 1 to 4, the process pressure was adjusted to a pressurelower than 10 Pa (3 Pa in these cases), and species and flow rate of gaswere varied. In Cases 1 and 3, nitrogen gas was used as the etching gasfor organic insulating film and a mixture of hydrogen gas (H₂) andnitrogen gas (N₂) was used. In Cases 2 and 4, ammonia gas was used as anetching gas for organic insulating film, and a mixture of hydrogen gas(H₂) and ammonia gas (NH₃) was used. In Case 1, the quantity of hydrogengas was 20 times that of nitrogen gas functioning as etchant for organicinsulating film. In Case 2, the quantity of hydrogen gas was 10 timesthat of ammonia gas functioning as etchant for organic insulating film.In Case 3, the quantity of hydrogen gas was the same as that of nitrogengas functioning as etchant for organic insulating film. In Case 4, thequantity of hydrogen gas was the same as that of ammonia gas functioningas etchant for organic insulating film. In Case 5, the same process gasas in Case 1 was used, and the process pressure was 10 Pa or more (10 Pain this case). Throughout all the cases, the power of high-frequencypower for plasma generation was 1 kW.

[0081] These experimental results demonstrate the following facts:

[0082] (1) Etch rate can be improved by using ammonia gas as etchinggas, as compared with the other case.

[0083] (2) Sub-trenching coefficient can be improved by increasing theproportion of hydrogen gas as compared with that of etchant gas. Theterm “sub-trenching coefficient” means the following ratio expressed interm of percentage:

[0084] (Etch Rate in Areas Near the Etched Sidewall/Etch Rate at Centerof Trench)

[0085] When the percentage defined above is 100% or less, it is knownthat no sub-trenching has occurred.

[0086] (3) For preventing the sub-trenching, it is necessary that themixing ratio of the H-component gas to the N-component gas (H-gas/N-gas)in the treating gas is 10 or more, the total flow rate is 200 cc/minuteor more, and the emission spectral intensity ratio (CN/H) is 1 or less.These conditions further mean that, in order to prevent thesub-trenching, the pressure in the etching process chamber has to belower than 10 Pa.

[0087] By measuring the emission spectral intensity of the plasma in thecases inducing no sub-trenching and the cases inducing sub-trenching, ithas been found that characteristic peaks of light emission intensityappear at wavelengths of 388 nm and 486 nm. These two spectra areassignable to cyan molecule (CN) having a wavelength of 388 nm andhydrogen atom (H) having a wavelength of 486 nm.

[0088] As a result, it can be concluded that the etching conditionsinducing no sub-trenching are those of Case 1 and Case 2. FIG. 5illustrates result of measurement of light emission intensities of cyanmolecule (CN) which is reaction product in the plasma formed under thesubtrenching-free conditions and hydrogen atom (H), wherein it is knownthat hydrogen atom (H) is higher than cyan molecule (CN) in lightemission intensity. The etching conditions in this case are as follows;H₂: 300 sccm, N₂: 10 sccm, pressure of treatment: 3 Pa, high-frequencypower for formation of plasma: 1 kW.

[0089] The fact that hydrogen atom (H) is higher than cyan molecule (CN)in light emission intensity means that, in the plasma, the quantity ofhydrogen atom (H) (in other words, H radical) is larger than thequantity of cyan molecule (CN). Thus, it is considered that the state ofreaction is as shown in FIG. 7. That is, in the plasma, the quantity ofH radical is larger than that of N ion as an etchant. Upon incidence ofN ion into the etched surface, the N ion reacts with organic insulatingfilm 44 to form cyan molecule CN as a reaction product. The cyanmolecule CN which has once left the wafer 2 again enters the wafer 2 andis deposited on the bottom surface of etched part. When H radicaloriginated from the plasma is contacted with the deposited CN molecule,there occurs a reaction to form a more volatile reaction product HCNwhich vaporizes from the etched surface and is exhausted. Thus, theprocess of etching progresses regardless of the influence of depositiondistribution of reaction product (in this case, cyan molecule CN) in theetched part (deposition distribution: the reaction product is morereadily deposited on the central part of trench than in the neighborhoodof sidewall), and thereby the sub-trenching can be prevented.

[0090] Contrariwise, sub-trenching occurs in the other cases (Case 3, 4and 5). If the light emission intensities of cyan molecule (CN) andhydrogen atom (H) in the plasma are measured and compared with thoseunder the conditions inducing sub-trenching, it is found that intensityof hydrogen atom (H) is lower than that of cyan molecule (CN) as shownin FIG. 6. The etching conditions in these cases are as follows; H₂: 35sccm, N₂: 35 sccm, treating pressure: 3 Pa, high-frequency power forgeneration of plasma: 1 kW. It is considered that the state of reactionis as shown in FIG. 8 under such conditions. That is, the plasmacontains a large quantity of N ion, and a high etch rate can beachieved. At the same time, the quantity of CN is also large, andre-deposition of CN onto the etched surface takes place. Since thereaction product is more readily deposited onto the central part ofbottom surface than in the bottom surface near the sidewall of etchedsurface, the bottom surface near the sidewall is more readily etched toinducing sub-trenching. Further, it is also considered that N ion havinga higher incidence energy into wafer is concentrated into theneighborhood of sidewall of the etched part, and thereby sub-trenchingoccurs.

[0091]FIG. 9 illustrates the relation between light emission intensityratio between cyan molecule (CN) and hydrogen atom (H), namely CN/H, andthe sub-trenching coefficient. It is understandable from FIG. 9 that theCN/H ratio at which the sub-trenching coefficient becomes 100% or lesswhere no sub-trenching occurs is 1 or less, roughly saying. Additionallysaying, the point in the case shown in Table 1 is the point to whichcase number is attached. The state of light emission intensity shown inFIG. 5 is point (a), and the state of light emission intensity shown inFIG. 6 is pint (b).

[0092] Next, the controlling method for preventing the sub-trenching bythe use of the controlling apparatus 31 shown in FIG. 1 is explained byreferring to FIG. 10.

[0093] In the above-mentioned Step 116 of the etching for forming wiringtrench in an organic insulating film, the emission spectra from the cyanmolecule CN and hydrogen atom H from the plasma are converted toelectric signals by means of a photoelectric converter, and therespective intensities are measured (Step 121). From the measuredintensities of CN and H, intensity ratio CN/H is calculated (Step 122).Subsequently, whether or not the intensity ratio CN/H is smaller than 1or less is judged (Step 123). If the judged intensity ratio is 1 orless, the etching is continued without changing the conditions (Step129). After continuing the etching, whether the desired quantity ofetching has been reached or not is judged according to theabove-mentioned method of end point detection using film thicknessmeasurement (Step 130). When the desired quantity of etching is not yetreached, the procedure is turned back to Step 121 and the processing iscontinued. When the quantity of etching has reached the desired valueand the end point of etching has been detected, the etching process iscompleted.

[0094] On the other hand, when emission intensity ratio is greater than1 in Step 123, the flow rate controlling valves are operated to increasethe flow rate of hydrogen gas (Step 124). Although it is also allowableto decrease the flow rate of nitrogen gas, such an operation causes adecrease in etch rate. Therefore, it is more desirable to change theflow rate of hydrogen gas. Although not shown in the figure, thecontroller 31 controls the gas exhaust rate controlling valve 27 so asto give a constant process pressure. Subsequently, whether or not thevalue of flow rate control has reached the upper limit, or maximum, isjudged (Step 125). So far as the value of flow rate control has notreached the maximum value, the procedure is turned back to Step 121, andcheck of intensity ratio is repeated.

[0095] In the case where the value of flow rate control is maximum andit is impossible to increase the quantity of hydrogen gas further, theelectric power for plasma generation is increased (Step 126). By takingsuch a measure, the decomposition of hydrogen molecule in the plasma isenhanced, a larger quantity of H radical is formed, and light emissionintensity of H radical is enhanced. Subsequently, whether the output ofthe high-frequency power from the high-frequency electric source forplasma generation is maximum or not is judged (Step 127). So far as theoutput of high-frequency power has not yet reached the maximum, theprocedure is turned back to Step 121 and the check of intensity ratio isrepeated.

[0096] On the other hand, in the case where the output of high-frequencypower is maximum and the power value cannot be enhanced further, outputof the high-frequency power of bias-application to wafer is lowered(Step 128).

[0097] As above, the control is carried out by increasing hydrogen gasin the first stage and increasing the power for plasma generation in thesecond stage. Accordingly, occurrence of sub-trenching is suppressedwithout lowering the etch rate-caused parameter. Thus, sub-trenching canbe prevented while maintaining the prescribed etch rate.

[0098] As has been mentioned above, according to the present example, aprocess pressure lower than 10 Pa is adopted, and the reaction productCN which is apt to be re-deposited at the time of etching is positivelyconverted to highly volatile HCN through reaction with the hydrogencomponent and then exhausted. Accordingly, the method of the presentexample has an effect that etching of organic insulating film can beperformed while preventing micro-trenching.

[0099] Further, according to the present example, in the etching oforganic insulating film having a low dielectric constant, trench or holecan be flattened without forming sub-trench, and therefore a trench forelectric wiring can be formed on semiconductor LSI chips without usingan etch stop layer.

[0100] Further, according to the present example, etching process oforganic insulating film can be carried out without sub-trenching byusing a mixture of nitrogen gas and hydrogen gas as a treating gas undera treating pressure lower than 10 Pa and controlling the light emissionintensity ratio between emission spectra of cyan molecule CN andhydrogen atom H in the plasma so as to come to 1 or less.

[0101] Further, by increasing and controlling the flow rate of hydrogengas so that the light emission intensity ratio CN/H comes to 1 or less,the sub-trenching can be suppressed without decreasing the etch rate oforganic insulating film.

[0102] Further, by increasing and controlling the output of thehigh-frequency power for plasma generation so that the light emissionintensity ratio CN/H comes to 1 or less, the quantity of H radical inplasma can be increased and thereby sub-trenching can be suppressedwithout lowering the etch rate of organic insulating film.

[0103] Further, since a gaseous mixture of nitrogen gas and hydrogen gasis used as the process gas, the gas formulation is simple, and the lightemission intensity ratio CN/H can easily be controlled by controllingthe flow rate of process gas.

[0104] In the present example, a mixture of nitrogen gas and hydrogengas was used as the process gas for trench-processing of organicinsulating film. However, the same effect as above can be obtained alsoby using a gaseous mixture of ammonia gas and hydrogen gas and makingthe light emission intensity ratio CN/H in the plasma come to 1 or less.

[0105] In the present example, an UHF magnetic field type plasma etchingapparatus using an electric source of frequency 450 MHz was used as thehigh-frequency electric source for plasma generation. However, the sameeffect as above can also be achieved with an apparatus of otherdischarge methods such as micro wave ECR, capacitive coupled, inductivecoupled, magnetron, etc., so far as the apparatus is capable of etchingan organic insulating film at a process pressure lower than 10 Pa, bybalancing between cyan molecule and hydrogen atom.

[0106] As above, according to this invention, there can be achieved aneffect that an organic insulating film can be etched while suppressingthe deposition of reaction product onto inside of process chamber andpreventing the microtrenching.

[0107] It should be further understood by those skilled in the art thatthe foregoing description has been made on embodiments of the inventionand that various changes and modifications may be made in the inventionwithout departing from the spirit of the invention and the scope of theappended claims.

What is claimed is:
 1. An etching method of an organic insulating filmcomprising: generating a plasma from a molecular gas containing hydrogenatom and nitrogen atom, measuring a light emission spectral intensityratio between hydrogen atom and cyan molecule in the plasma, andcarrying out an etching process while keeping the measured value at avalue not exceeding a prescribed value.
 2. The etching method of organicinsulating film according to claim 1 comprising: keeping a lightemission spectral intensity ratio CN/H at 1 or less, wherein Hrepresents a light emission spectral intensity of hydrogen atom at awavelength of about 486 nm and CN represents a light emission spectralintensity of cyan molecule at a wavelength of about 388 nm in theplasma.
 3. An etching method of an organic insulating film comprising:generating a plasma from a hydrogen gas and a nitrogen gas or an ammoniagas, and carrying out the etching process while controlling a flow rateof the hydrogen gas so that a light emission spectral intensity ratiobetween hydrogen atom and cyan molecule in the plasma comes to a valuenot exceeding a prescribed value.
 4. The etching method of organicinsulating film according to claim 3, wherein said process is carriedout while controlling the pressure of processing so as to come to aconstant pressure.
 5. An etching method of an organic insulating filmcomprising: feeding a molecular gas containing a nitrogen gas and ahydrogen gas or a molecular gas containing hydrogen atom and nitrogenatom into an etching process chamber in which a sample to be etchedhaving an organic insulating film formed thereon has been placed,adjusting a pressure in the etching process chamber to a pressure lowerthan 10 Pa, generating a plasma in which a light emission spectralintensity ratio CN/H is 1 or less, wherein H represents a light emissionspectral intensity of hydrogen atom at a wavelength of about 486 nm andCN represents a light emission spectral intensity of cyan molecule at awavelength of about 388 nm, and processing the sample to be etched withsaid plasma.
 6. The etching method of an organic insulating filmaccording to claim 5, wherein a hydrogen gas and a nitrogen gas are usedfor a formation of said plasma and a mixing ratio of said hydrogen gasto said nitrogen gas is 10 or more.
 7. The etching method of an organicinsulating film according to claim 6, wherein the total flow rate ofsaid hydrogen gas and said nitrogen gas is 200 cc/minute or more.
 8. Theetching method of an organic insulating film according to claim 5,wherein said molecular gas containing hydrogen atom is a hydrogen gas,said molecular gas containing nitrogen atom is an ammonia gas, and amixing ratio of said hydrogen gas to said ammonia gas is 10 or more. 9.The etching method of an organic insulating film according to claim 8,wherein the total flow rate of said hydrogen gas and said ammonia gas is200 cc/minute or more.